Abstract

Passive acoustic monitoring (PAM) involves the recording, observing, and analyzing of sound production of soniferous species for the purposes of ecological monitoring. PAM is especially useful for monitoring soniferous species that form fish spawning aggregations (FSAs) and can be difficult to observe outside of these seasonal aggregations. Nassau grouper, Epinephelus striatus, are one such soniferous species and are known to make three distinctive call types including a territorial call made outside spawning season, a courtship-specific call, and an agonistic call type made between two males during spawning aggregations (Schärer et al., 2012; Rowell et al., 2018; Wilson et al., 2020). Additionally, they are considered one of the most well-documented case studies of a drastic decline in population due to overfishing at FSAs. Following their protection in US federal waters, Nassau grouper have been documented undergoing local population recovery at the Grammanik Bank FSA, which is a 1.5 km2 seasonal fishery closed area located 10 km south of St Thomas, US Virgin Islands. For the past 11 years (2012-2023), passive acoustic data has been collected at fixed points along the Grammanik Bank using DSG and Cyclops audio recorders (Loggerhead Instruments). In this study, we analyzed the call patterns of Nassau grouper to see if they change alongside the changes in the number of individuals visually recorded at the FSA over time. Linear modeling identified a positive relationship between the number of Nassau grouper at the FSA and the number of Nassau grouper courtship-associated sounds (CAS) calls at the FSA (p = 0.02). This work demonstrates that PAM is a useful tool in the ongoing monitoring and management of the Grammanik Bank population of Nassau grouper, and has the potential to be used to estimate population sizes of other recovering FSA sites where no monitoring is happening or no baseline data has been collected.

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